In the past, in some image display devices having an on-screen display (hereinafter referred to as “OSD”) function, the number of pixels in a region on a display screen, the region in which OSD display is performed, that is, the size of an OSD display region has been set at a fixed size. Moreover, the number of pixels of a character used in the OSD display, that is, the size of an OSD display character has also been set at a fixed size. The sizes of the OSD display region and the OSD display character have been set as fixed values in advance in an OSD display control program product for realizing the OSD function. When such an OSD display control program product is used in another image display device having a different total pixel number of the display screen, the OSD display region becomes small or large relative to the size of the display screen. This sometimes makes it impossible to recognize the OSD display character or results in poor viewability.
Patent Document 1 discloses an image display device (a composite image output device) which can store, according to size, image data of characters to be displayed on the screen of a display device by the OSD function and allow the user to display the character by setting and changing the size of the character.